1. Field of the Invention
The present invention relates to an analogue measurement data detection system and particularly to a battery voltage detection system configured to detect voltages of in-vehicle lithium ion batteries.
2. Description of the Related Art
One of the measures for assuring the safety of a battery module in which a plurality of battery cells are connected in series is to manage the voltage of each of the plurality of battery cells (hereinafter, referred to as a cell voltage). One specific example is to perform charge-discharge control based on a measured value of each cell voltage. Among various secondary batteries, lithium ion batteries in particular are mainly used as batteries to be installed in hybrid electric vehicles (HEV) and electric vehicles (EV) for the reason that lithium ion batteries have a higher output voltage, higher energy density, and higher efficiency than other secondary batteries. However, it is difficult to control charging and discharging of lithium ion batteries, and lithium ion batteries are known to have a risk of explosion and firing. Therefore, in a case where a lithium ion battery is used as an in-vehicle battery, taking various safety measures regarding charge-discharge control is essential.
For example, Japanese Laid-Open Patent Application Publication No. 2010-60435 proposes a battery voltage detection system configured to detect battery cell voltages with high precision. FIG. 8 shows a configuration of the battery voltage detection system disclosed in Japanese Laid-Open Patent Application Publication No. 2010-60435. In the battery voltage detection system shown in FIG. 8, battery cells CEL1 to CELn are connected in series. Voltages at terminals of the battery cells CEL1 to CELn are supplied to respective voltage input nodes NC0 to NCn. Switches SA0 to SAn and SB0 to SBn of a switching unit 10 turn ON or OFF connections between the voltage input nodes NC0 to NCn and detection input nodes NA and NB based on control by a controller 50. A voltage detector 20 is configured to generate a voltage detection signal S20 in accordance with a difference between voltages inputted to the respective detection input nodes NA and NB. An analogue/digital converter 30 is configured to convert the voltage detection signal S20 outputted from the voltage detector 20 into digital data with a predetermined bit length. A detection data processor 40 is configured to generate voltage detection data S40, which indicates a precise voltage of each of the battery cells CEL1 to CELn, based on digital data S30 outputted from the analogue/digital converter 30. The controller 50 is configured to control the switching unit 10 to detect the voltage of each of the battery cells CEL1 to CELn by means of the voltage detector 20. Specifically, the controller 50 is configured to sequentially select one of the battery cells CEL1 to CELn, and connect a pair of voltage input nodes connected to positive and negative electrodes of the selected battery cell to the detection input nodes NA and NB in two patterns (forward connection and reverse connection).